Conventionally, a power supply line, associated with a communication path used for mutual communication between electronic devices, has been used for an electronic device having no power source to receive electric power from an electronic device with a power source. The power supply line almost has not been used for charging a battery-driven electronic device.
In recent years, devices to charge a battery driven electronic device using this power supply line have been proposed as disclosed in Japanese Patent Application Laid-Open Nos. 2002-044876 and 2002-191133. However, these devices relate to an electronic device which fixedly operates as a slave.
Further, in a recently-proposed system having plural electronic devices interconnected via a communication line, the master-slave relation is dynamically switched over in accordance with operational status at any given time.
However, the conventional power supply method, for merely charging a slave device in fixed master-slave relation by using a power supply line associated with a communication path, cannot be applied to the above system.